1. Field of the Invention
The present invention relates to a method and apparatus for transmitting signals by using chaotic signals having an orthogonal property in a wireless or wired communication system.
2. Description of the Prior Art
Multiple access is a method for accessing a particular resource when a plurality of devices request resources whose quantity is limited. Herein, the resources signify all elements needed for communication. Take, for example, a base station in a wireless sector. A plurality of terminals attempt to access one base station, and collision occurs when the multiple terminals request access to a limited frequency and equipment of the base station. One of the methods for preventing the collision is random access but other diverse methods are also available.
The multiple access includes Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), and Time Division Multiple Access (TDMA).
The FDMA is a technique for communication in which an allocated frequency band is divided into sub-bands and a corresponding sub-band is assigned to a terminal attempting to communicate. A representative technique of the FDMA is an Advanced Mobile Phone Service (AMPS), which is the initial analogue mobile telephony.
The TDMA is a technique in which a frequency is temporally divided and used. In TDMA, a frequency is divided into a sequence of time slots and each time slot is allocated to a subscriber. A well-known example of the TDMA is the Global System for Mobile Communication (GSM) and the Narrow-AMPS (N-AMPS), which are used in Europe.
The CDMA divides a frequency into channels by using codes in a wireless sector. Of course, each channel uses the same frequency band and the same frequency width. Since each channel is operated by electric wave energy in the wireless sector according to the intensity of electric wave, a channel using strong electric waves has much energy. In other words, to discriminate between subscribers, the CDMA uses different pseudo noise (PN) codes of the same length.
FIG. 1 shows a conventional transmitter for multiple access using chaotic signals. The transmitter attempting multiple access by using chaotic signals includes a chaotic signal generator 100, a delay unit 102, a multiplier 104, and a multiplexer 106.
The chaotic signal generator 100 generates chaotic signals. The characteristics of chaotic signals will be described later. The chaotic signals generated in the chaotic signal generator 100 are output to the multiplexer 106 and the delay unit 102.
The delay unit 102 delays the transmitted signals for a certain time, which may be predetermined, and then outputs the delayed signals to the multiplexer 106 and the multiplier 104. The multiplier 104 multiplies the signals by −1 and outputs the result to the multiplexer 106. The multiplexer 106 receives the signals from one of the delay unit 102 and the multiplier 104 at a specific time point. The multiplexer 106 outputs one of the received signals upon receipt of a control signal. Hereafter, the signals output from the transmitter for multiple access using the chaotic signals will be described.
FIG. 2 presents signals transmitted from four subscribers. The four subscribers are a subscriber 1, a subscriber 2, a subscriber 3, and a subscriber 4. The reference ‘R’ of FIG. 2 denotes a reference signal and the reference ‘D’ denotes data. The transmission length of the reference signal is the same as that of the data. Therefore, although FIG. 2 illustrates only one delay unit, when the four subscribers are to transmit signals, the number of delay units becomes four.
Also, the reference ‘R1, 1’ denotes a signal that the transmission subscriber 1 transmits to a reception subscriber 1, and the reference ‘R2, 1’ denotes a signal that a transmission subscriber 2 transmits to the reception subscriber 1. In FIG. 2, the transmission subscriber 1 transmits data after delaying the data for a first delay time, compared to the reference signal, and the transmission subscriber 2 transmits data after delaying the data for two times the first delay time, compared to the reference signal. Also, the transmission subscriber 3 transmits data after delaying the data for three times the first delay time, compared to the reference signal, and the transmission subscriber 4 transmits data after delaying the data for four times the first delay time, compared to the reference signal.
In short, the delay unit differentiates the delay time for each transmission subscriber. The delay unit of the transmission subscriber 1 outputs the data after delaying them for the first delay time, while the delay unit of the transmission subscriber 2 outputs the data after delaying them for two times the first delay time. Also, the delay unit of the transmission subscriber 3 outputs the data after delaying them for three times the first delay time, while the delay unit of the transmission subscriber 4 outputs the data after delaying them for four times the first delay time.
FIG. 3 shows a structure of the receiver. The receiver includes a delay unit 300, a multiplier 302 and an accumulator 304. The delay unit 300 delays data among the transmitted signals for a certain time and transmits the data to the multiplier 302. This certain time may also be predetermined. The multiplier 302 multiplies the data received from the delay unit 300 by the reference signal received from the transmitter and outputs the multiplied signals to the accumulator 304. The accumulator 304 accumulates the transmitted signals. Hereafter, the operation of the delay unit 300 will be described with reference to FIG. 2.
The delay unit 300 in the receiver transmits signals corresponding to data among the transmitted signals directly to the multiplier 302 to recover the signals transmitted from the transmission subscriber 1 and transmits the reference signal to the multiplier 302 after delaying it for the first delay time. This way, the multiplier 302 can acquire desired signals by receiving the data and the reference signal at the same time point.
The delay unit 300 of the receiver transmits signals corresponding to data among the transmitted signals directly to the multiplier 302 to recover the signals transmitted from the transmission subscriber 2 and transmits the reference signal to the multiplier 302 after delaying it for 2× the first delay time.
The delay unit 300 of the receiver transmits signals corresponding to data among the transmitted signals directly to the multiplier 302 to recover the signals transmitted from the transmission subscriber 3 and transmits the reference signal to the multiplier 302 after delaying it for 3× the first delay time.
The delay unit 300 of the receiver transmits signals corresponding to data among the transmitted signals directly to the multiplier 302 to recover the signals transmitted from the transmission subscriber 4 and transmits the reference signal to the multiplier 302 after delaying it for 4× the first delay time.
As described above, the receiver uses delay times established differently according to each transmission subscriber to acquire the signals transmitted from a particular transmission subscriber. The more transmission subscribers there are, the longer the delay time becomes. Therefore, there is a problem that the structure of the delay unit is complicated as the number of transmission subscribers is increased.